Apparatus for grinding drills

ABSTRACT

Apparatus is described whereby the clearance surfaces of the working head of a drill are ground by keeping the drill axis at an operatively constant angle relative to the rotary place of a grinding wheel, while rotating the drill about its longitudinal axis within a limited angular area. In one embodiment of the invention the wheel heel is provided with a single grinding surface and may be mounted stationary or mounted to yield against spring pressure to a single clearance surface urged against it, until the other clearance surface is intercepted by an abutment upon which it rests while rotating the drill, thus providing an essentially steady grinding pressure. In the latter case, the point of the drill will be centrically ground after working each clearance surface for an equally long time. In a modified form the wheel is provided with two conical grinding surfaces and a slight clearance between these surfaces. Thereby a centrically ground point of the drill is automatically achieved.

United States Patent [1 1 Wurscher APPARATUS FOR GRINDING DRILLS [75]Inventor: Raimund August Wurscher, Lund,

Sweden [73] Assignee: Intermedium AG, Luegisland,

Sweden [22] Filed: Aug. 4, 1970 [21] Appl. No.: 60,888

Related US. Application Data [30] Foreign Application Priority Data May3, 1967 Sweden 6201/67 [52] US. Cl 51/73 R, 51/102, 51/128, 51/219 R[51] Int. Cl. B241) 3/26 [58] Field of Search 51/73 R, 102, 128, 51/219R, 241 R 5 6] References Cited UNITED STATES PATENTS 1,231,258 6/1917Horvath 5l/2l9RX 1,994,975 3/1935 Wil1iams..... 51/73 R UX 2,017,53210/1935 Elter et a1... 51/219 R X 2,372,794 4/1945 Ricks 51/219 R X2,424,470 7/1947 Kronwall..... 51/219 R X 2,540,320 2/1951 Cayo 51/73 RX 2,591,893 4/1952 Trippel.... 51/219 R X 2,601,748 7/1952 Lohr 51/219 RX I I '2 x 1 l3 1 II 1 Aug. 21, 1973 Perra 51/219 R X PrimaryExaminer-Donald G. Kelly Attorney-Jacobs & Jacobs [57] ABSTRACTApparatus is described whereby the clearance surfaces of the workinghead ofa drill are ground by keeping the drill axis at an operativelyconstant angle relative to the rotary place of a grinding wheel, whilerotating the drill about its longitudinal axis within a limited angulararea. In one embodiment of the invention the wheel heel is provided witha single grinding surface and may be mounted stationary or mounted toyield against spring pressure to a single clearance surface urgedagainst it, until the other clearance surface is intercepted by anabutment upon which it rests while rotating the drill, thus providing anessentially steady grinding pressure. In the latter case, the point ofthe drill will be centrically ground after working each clearancesurface for an equally long time. In a modified form the wheel isprovided with two conical grinding surfaces and a slight clearancebetween these surfaces. Thereby a centrically ground point of the drillis automatically achieved.

32 Claims, 7 Drawing Figures msmcomz I m 3753.320 sum 1 0F 33 INVENTORRAIMUND AUGUST WURSCHER ATTORNEYS mcmznwm m 3.753.320

sum 3 BF 3 PEG. 2

INVENTOR RAIMUND AUGUST WURSCHER FIG. 5 BY A a! ATTORNEYS l APPARATUSFOR GRINDING. DRILLS.

This application is a continuatiomin-part of application Ser. No.682,406, filed Nov. 13, 1967, now abancloned, and of application Ser.No. 27,589, filed Apr. 13, 1970, now abandoned, which, in turn, is acontinuation-in-part of said application Ser. No. 682,406 and ofapplication Ser. No. 864,445, filed Oct. 7, 1969, now abandoned.

The present invention relates to an app ratus for grinding drills, moreparticularly spiral drills.

In order that a drill may operate, quickly and efficiently and have along life, it is necessary to. grind the working head. of the drill in acorrect manner. In.-. creased drilling costs and faulty bores are mostlycaused by faulty grinding of the drill. Machine grinding is the mostexact method of grinding drills, and'when a drill is carefully machineground it will cut morev quickly, have a longer life and drill agreaternumber of exact bores than if it is ground manually. The most importantfactors for the efficiency of a drill, are. the point angle, theclearance angle, and the angle between the main cutting edges and thetransversal cutting edge of the drill head, the so-called transversalcutting edge angle. All these angles may be affected by the grinding ofthe drill head, is. at the grinding of the clearance sur face for eachmain cutting edge of the drill head.

In known apparatus for grinding drills it is generally necessary toclamp fast the drill to be ground, and the, known apparatus requireeither greater manual skill or else do not permit the drill headtooccupy the most advantageous clearance and transversal cutting edgeangles.

An object of the invention is to provide an apparatus for grindingdrills which does not make it necessary to clamp fast the drill whichis. being ground, but which will nevertheless guide, the drill, therebyachieving correct grinding of the drill head,

Another object of the invention is to provide an apparatus for grindingdrills of different diameters without readjusting the apparatus.

With the invention is provided an apparatus for grinding drill headshaving at least one main cutting edge and, in related cases, atransversal cutting edge intersecting the main cutting edges, and aclearance surface and a flute for each main cutting edge, comprising arotating grinding wheel provided with one or two grinding surfaces andat least one set of guiding means for guiding a drill in relation to thewheel, the guiding means having means for providing an essentiallyconstant operative angle between the geometrical longitudis nal axis ofthe drill and the rotary plane of the wheel and admitting a rotation ofthe drill about said axis, and means. li i g sa d o at on o ha a cearanc surface ill be w p but by a r ng u ace at such n relative to saidgrinding surface that the intended clearance angle of the clearancesurface is achieved.

In the preferred embodiment of the invention the guiding means of eachsaid set consists of a cylindrical guiding passage provided in a guidingelement and at least one guide lug mounted in the guiding passage forfitting into a flute of the drill.

The drill to be ground is inserted into the guiding passage in betweenthe guide lugs, pressed against the grinding surface or surfaces whilesimultaneously rotated in a reciprocating rotary movement limited by theguide lugs.

Where the grinding wheel is provided with one grinding surface, thegrinding operation has to be repeated for each clearance surface and, inorder to achieve a centered point of the drill, each clearance surfacehas to be ground for an equally long time under the same grindingpressure. For achieving a steady grinding pressure, the wheel ispreferably mounted so as to resiliently yield to a drill urged againstthe grinding surface, at which the advance of the 'drill is'interceptedby an abutment for engaging a clearance surface not engaging thegrinding surface; thus centering the drill point is, permitted bygrinding the clearance surfaces for an equally long time.

Where the grinding wheel is provided with two grinding surfaces, thecommon standard drill, having two clearance surfaces, will, regardlessof grinding pressure or grinding time, be automatically centered. Whereproviding a slight clearance between said two grinding surfaces, thetransversal cutting edge angle will be considerably improved.

In the accompanying drawings:

FIG. 1 a is a longitudinal section of an apparatus showing a grindingwheel provided with one grinding surface while grinding one clearancesurface of a drill;

FIG. lb is a longitudinal section of an apparatus showing a grindingwheel provided with two grinding surfaces while grinding the clearancesurfaces of a drill;

FIG. 1c is a longitudinal section of another embodiment of theinvention;

FIG. 2 is a plan view on a larger scale of a guiding passage havingguide lugs for limiting the rotation of the drill;

FIGS. 3 and 4 show the same detail as FIG. 2 although with the workinghead of the drill drawn in the two limiting positions of the rotationalmovement occurring during the grinding operation, the plan view of FIGS.2 to 4 being seen in a direction towards the grinding wheel from thebase of the drill; and

FIG. 5 is a plan view of the working head of the drill.

The drill 1 shown in the drawings is assumed to be held and handledmanually during the grinding operation. The main parts of the grindingapparatus are enclosed in a tubular housing 2 open at both ends. Thehousing is inserted into and attached to a flange 4 screwed into. thefront wall of an electric motor 3. In FIG. la the grinding wheel 5 hasone conical grinding surface and is fixed to a tubular grinding wheelshaft 6 by means of a nut 7. The grinding wheel shaft 6 is threaded ontothe driving shaft 8 of the electric motor 3 so that their twolongitudinal axes will coincide with the longitudinal axis of thetubular housing 2 and will be parallel to the longitudinal axis of thedrill head 1. The grinding wheel shaft 6 and consequently also thegrinding wheel 5 are axially movable in relation to the driving shaft 8of the electric motor 3 and are urged by spring 9 in the direction ofthe head of the drill 1. Power is transmitted to the grinding wheelshaft 6 by means of a pin 10 fixed to the grinding wheel shaft 6 andengaging with a slot 11 provided in the end of the driving shaft 8. Intothe end of the housing 2 which is remote from the motor 3 there isintroduced a cylindrical guiding element 12 fixed with a clamping screw13. The guiding element 12 has cylindrical guiding passages at the samecenter distance from and parallel to the grinding wheel shaft 6, forguiding drills of different diameters, two of which, 14 and 15, areshown in FIG. 121. At the end of the guiding element 12 which is remotefrom the grinding wheel 5 there is provided an abutment element 16common to all guiding passages 14, and intended for that clearancesurface of the drill head which is not in contact with the grindingwheel 5. The abutment element 16 has an oblique surface extending alonga helical line, the central axis of which coincides with the rotationalaxis of the grinding wheel 5 and the peripheral radius of which isslightly shorter than the radius of the circle cutting the center axesof all guiding passages 14, 15.

The widest guiding passage is directed towards that point of the face ofthe abutment element 16 which is nearest to the grinding wheel 5, whilethe narrowest guiding passage is directed towards that point of the saidface which is most remote from the grinding wheel 5 as urged to itsremotest distance from the guiding element l2, and the other guidingpassages are distributed between the widest and the smallest oneaccording to their diameters. This provides for a correct setting of thedrill heads in relation to the grinding wheel and for approximately thesame stable grinding pressure, irrespective of the different diametersof the drill heads.

At the ends of the guiding passages which are directed to the face ofthe abutment element 16, there are provided two guide lugs 17, 18 (FIG.2) each fitting into one of the two spiral flutes of the drill 1. Theseare two trapezoidal mirror images of each other, displaced rotationallythrough 180 and each extending inwards approximately one fourth of aguiding passage diameter towards the center of the guiding passage 14,15They have each two straight abutment margins extending along twodifferent guiding passage diameters having a relative angle of 60 andare oriented so as to be symmetrically mirrored at each side of theradius 19 of the grinding wheel 5 through the center axis of therespective guiding pasasge 14, 15. They are disposed at a distance fromthe corresponding part of the face of the abutment element 16 which isequivalent to an angular difference of 2 between the drill diameter thatmeets the extreme corners of the main cutting edges 20 and the drilldiameter meeting the guiding margins of the flutes of the drill in thelimiting plane of the guide lugs 17 and 18 through their abutmentmargins.

The distance of the abutment element 16 to the guiding pins 17 and 18may be adjusted by turning a knob 23 at the upper end of a shaft 22carrying the abutment element 16. Into the central portion of the shaft22 there is screwed an abutment 24 for the grinding wheel shaft 6,limiting the resilient movement of the grinding wheel in a directiontowards the guiding element 12 when no drill is being ground.

The drill I inserted into a guiding passage suitable therefor is pressedfor grinding one of its clearance surfaces against the face of theabutment element 16 while simultaneously rotated in a reciprocatingrotary movement so limited by the guide lugs 17 and 18 that the diameterof the drill which meets the extreme comers of its main cutting edges 20in the two limiting positions of the rotary movement forms the angles ofabout 62 (,8, in FIG. 3) and 32 (B, in FIG. 4) with the radius 19 of thegrinding wheel through the center of the drill 1, at which a transversalcutting edge angle of about 50 y in FIG. 5) is obtained. Thereby aclearance angle of about 12 is obtained, somewhat depending on thediameter of the grinding wheel, its pitch angle a, etc. When thedistance between the abutment element 16 and the guide lugs 17 and 18 ischanged by means of the knob 23, the guide lugs will engage with aportion of the drill flutes that is located higher or lower, and theangular area within which the clearance surface being ground can berotated, will be tuned in relation to the radius 19 of the grindingwheel so that other clearance angles may be obtained.

If the power with which the spring 9 urges the grinding wheel 5 againstthe working end of the drill is the same for drills of differentdiameters, the grinding pressure and consequently the grinding action inthe longitudinal direction of the drill is approximately inverselyproportional to the square of the drill diameter. This may, however,entail difficulties when centering small drill heads, since thecentering is achieved by grinding both clearance surfaces for an equallength of time and is thus dependent on time. It is therefore desirablethat the grinding pressure is-not changed together with the drilldiameter, which may be achieved by loading the spring 9, i.e.compressing it proportionally to the square of the drill diameter. Thisis possible in the above embodiment of the abutment element 16 and thecollateral distribution of the guiding passages 14, 15 in the guidingelement 12, provided the uncompressed spring 9 is of suitable length.

FIG. 1b shows the embodiment of the invention wherein the grinding wheel5 is provided with two grinding surfaces 5a and 5b with a slightclearance 19 along the meeting circular border of these surfaces. Thegrinding wheel 5 is fixed to a nave 6 which, in turn, is fixed to thedriving shaft 8 of the electric motor 3 so that the rotational axis ofthe wheel will coincide with the longitudinal axis of the housing 2 andwill be parallel to the axis of the drill 1'. In the threaded end of thehousing 2 which is remote from the electric motor 3, a cylindricalguiding element 12 is screwed on and fixed with a clamping screw 13. Theguiding element 12 has cylindrical guiding passages, parallel with andat a common distance from the rotational axis of the wheel equal to theradius of the circular border between the internal and the externalconical grinding surfaces of the wheel, for guiding drills of differentdiameters, two of which, 14 and 15, are shown in the drawing.

The drill I inserted into the guiding passage suitable therefor is, forgrinding its clearance surfaces, pressed against the grinding surfacesas turned in a reciprocating rotary movement limited by the guide lugs,whereby the clearance surfaces move within an angular area so sized andso disposed relative to the grinding surfaces that each of the clearancesurfaces will obtain the intended clearance angle.

By screwing the guiding element 12 in or out, the distance between theguide lugs 17', 18 and the grinding surfaces can be altered and otherclearance angles of the clearance surfaces will be obtained.

It is to be understood that the guiding passages need not be parallelwith the rotational axis of the wheel, but may be inclined to said axisat any angle. They only have to guide the drills against the grindingsurfaces such as to tally with the inclination of the grinding surfacesand to guide the point of the drill onto the border between the twogrinding surfaces as illustrated in FIG. lb. Accordingly, the shapes ofthe grinding surfaces may be other than as illustrated; for instanceboth of them may have an external conical shape as illustrated in FIG.1c.

FIG. 1c employs the same reference numerals as FIGS. 1a and lb todesignate like parts, but the reference numerals are double primed inFIG. 1c.

What is claimed is:

1. Apparatus for grinding drills having at least'two main cutting edgesand having a clearance surface for each main cutting edge, comprising arotatable grinding wheel provided with at most two grinding surfaces andat least one set of guiding means for guiding a drill head in relationto the wheel, the guiding means having means for providing anessentially constant operative angle between the geometricallongitudinal axis of the drill and the rotary plane of the wheel andadmitting a rotation of the drill about said axis, at least one firststop means for engaging the drill and thereby preventing rotation of thedrill about its axis in one direction beyond a first limiting positionand at least one second stop means for engaging the drill and therebypreventing rotation of the drill about its axis in a direction oppositeto said one direction beyond a second limiting position, said first andsecond stop means being so arranged with respect to one another and to adrill in said guiding means as to be operable to limit said rotation ofsaid drill to a predetermined angular extent between a said first andsecond limiting positions such that when said drill is rotated betweensaid limiting positions and through said predetermined angular extentwhile a clearance surface thereof is in contact with an associatedrotating grinding surface a predetermined clearance angle and apredetermined transversal cutting edge angle are both obtained. 1

2. Apparatus according to claim 1, wherein each set of guiding meansconsists of a cylindrical guiding passage provided in a guiding elementand said first and second stop means are provided by at least one guidelug having a pair of oppositely disposed abutment margins and beingassociated with the guiding passage for fitting into a flute of a drill,rotation of the drill about its axis in said one direction beyond saidfirst limiting position being prevented by engagement of said drill withone of said abutment margins and rotation of the drill about its axis insaid opposite direction beyond said second limiting position beingprevented by engagement of said drill with the other abutment margin.

3. Apparatus according to claim 2, wherein there is provided a number ofguiding passages and guide lugs associated therewith, which guidingpassages have different diameters for guiding drills. of differentdiameters.

4. Apparatus according to claim 3, further provided with means wherebythe wheel, by increasing resistance, resiliently recoils to the pressureexerted by at least one clearance surface urged against itscorresponding grinding surface, and means for so intercepting theadvance of the drill as to determine a substantially steady operativedistance between the tip of the drill and the guide lugs and a stableresilient counterforce of the wheel.

5. Apparatus according to claim 4, wherein the wheel is provided withone grinding surface and the means intercepting the advance of the drillconsists of an abutment for receiving the clearance surface not engagingthe grinding surface.

6. Apparatus according to claim 5, wherein the abutments are united inone abutment element having a stop face advancing helically in thedirection of the rotational axis of the wheel at a common distance fromsaid axis, and wherein the guiding passages are so distributed accordingto their diameters over said stop face that a drill, inserted into itsappropriate guiding passage and urged onto the stop face, will cause thewheel to recoil a distance which is so increased by increased drilldiameter that the resilient counterforce of the wheel will produceapproximately the same grinding pressure for any drill that isreceivable.

7. Apparatus according to claim 6, further provided with means wherebythe distance between the stop face and the guide lugs can be varied.

8. Apparatus according to claim 1, wherein the wheel is provided withtwo conical grinding surfaces meeting along a circular border at anangle appropriate to the point angle of the drill.

9. Apparatus according to claim 8, wherein there is a slight clearancebetween the grinding surfaces along the meeting circular border of thesesurfaces.

10. Apparatus according to claim 8, wherein each set of guiding meansconsists of a cylindrical guiding passage provided in a guiding elementand said first and second stop means are provided by at least one guidelug having a pair of oppositely disposed abutment margins and beingassociated with the guiding passage for fitting into the flute of adrill, rotation of the drill about its axis in said one direction beyondsaid first limiting position being prevented by engagement of said drillwith one of said abutment margins and rotation of the drill about itsaxis in said opposite direction beyond said second limiting positionbeing prevented by engagement of said drill with the other abutmentmargin.

11. Apparatus according to claim 10, wherein is provided a number ofguiding passages and guide lugs associated therewith, which guidingpassages have different diameters for guiding drills of differentdiameters.

12. Apparatus according to claim 11, wherein there is a slight clearancebetween the grinding surfaces along the meeting circular border of thesesurfaces.

13. Apparatus according to claim 12, further provided with means wherebythe distance between the grinding surfaces and the guide lugs isadjustable.

14. Apparatus for grinding spiral drill bits having at least one maincutting surface and having a clearance surface and a flute for each maincutting surface, comprising a rotatable grinding wheel having a grindingsurface and means for connecting the wheel to a driving device and meansfor guiding a drill bit in relation to the grinding surface, the guidingmeans having means providing a constant angle between the geometricallongitudinal axis of the drill and the grinding surface during thegrinding operation, at least one first stop means for engaging the drilland thereby preventing rotation of the drill about its axis in onedirection beyond a first limiting position and at least one second stopmeans for engaging the drill and thereby preventing rotation of thedrill about its axis in a direction opposite to said one directionbeyond a second limiting position, said first and second stop meansbeing so arranged with respect to one another and to a drill in saidguiding means as to be operable to limit the rotational movement of thedrill bit to a predetermined angular extent between said first andsecond limiting position such that when said drill is rotated betweensaid limiting positions and through said predetermined angular extentwhile a clearance surface thereof is in contact with an associatedrotating grinding surface a predetermined clearance angle and apredetermined transversal cutting edge angle are both obtained.

15. Apparatus for grinding spiral drill bits having at least one maincutting surface, a transversal cutting surface intersecting the maincutting surface and one clearance surface and a flute for each maincutting surface, comprising a rotatable wheel having a bowlshapedconical grinding surface and having means for connecting the wheel to adriving device, a guiding element fixed in relation to the rotationalaxis of the wheel, a number of cylindrical guiding passages havingdifferent diameters one of which is largest and one of which is smallestprovided in the guiding element at equal distances from the rotationalaxis of the wheel and extending in parallel thereto, for guiding drillbits of different diameters in relation to the grinding surface, guidingpins in the guiding passages adapted to engage each with one of theflutes of the drill bits in order to limit the rotational movement ofthe drill bits between two limiting positions corresponding to thepoints of engagement of said flutes and said pins, said pins being soarranged with respect to one another and to a drill bit in said guidingpassage as to be operable to limit said rotation to a predeterminedangular extent between said limiting positions such that when said drillis rotated between said limiting positions and through saidpredetermined angular extent while a clearance surface thereof is incontact with an associated rotating grinding surface a predeterminedclearance angle and a predetermined transversal cutting edge angle orboth obtained and an abutment united with the guiding element fordetermining the position of the drill bits in relation to the guidingpins.

16. Apparatus as claimed in claim 15, wherein the wheel is mounted forresilience in an axial direction under the influence of the pressurefrom a drill bit pressed against the grinding surface, the pressure ofthe drill bit against the grinding surface being limited by the abutmentfor providing a constant grinding pressure.

17. Apparatus as claimed in claim 15, wherein the guiding passages areof essentially the same diameter as the drill bit.

18. Apparatus as claimed in claim 15, wherein the guiding pins aredisposed diametrically opposite each other in the guiding passage andextend inwards approximately one fourth of a guiding passage diametertowards the center of the guiding passage and being each provided withtwo straight abutments margins extending along two different diametersof passage forming an angle of 60 with each other.

19. Apparatus as claimed in claim 15, wherein the distance between theabutment and the guiding pins in the direction of the geometrical axisof the wheel is adjustable in order to provide different clearanceangles for the clearance surfaces of the drill bits.

20. Apparatus as claimed in claim 15, wherein the abutment is common toall guiding passages and extends along a helical turn, the center axisof which coincides with the rotational axis of the wheel and the radiusof which is slightly shorter than the radius of the circle cutting thecenter axes of all guiding passages.

21. Apparatus as claimed in claim 15, wherein the largest guidingpassage is directed towards that point of the abutment which is nearestto the grinding surface, while the smallest guiding passage is directedtowards the point that is most remote therefrom, while the other theguiding guiding passages are distributed therebetween according to theirdiameters.

22. Apparatus for grinding drills having at least one main cuttingsurface and one clearance surface and a flute for each cutting surfacecomprising a rotatable wheel having a conical grinding surface, meansconnected to the wheel for driving the wheel, a guiding element, atleast one cylindrical guiding passage provided in the guiding elementfor guiding drill bits in relation to the grinding surface, at least onefirst stop means in the guiding passage for engaging a flute of a drillwithin the guiding passage and thereby preventing rotation of the drillabout its axis in one direction beyond a first limiting position and atleast one second stop means in the guiding passage for engaging a fluteof the drill and thereby preventing rotation of the drill about its axisin a direction opposite to said one direction beyond a second limitingposition, said first and second stop means being so arranged withrespect to one another and to a drill within the guiding passage as tobe operable to limit the rotational movement of the drill to apredetermined angular extent between said first and second limitingpositions such that when said drill is rotated between said limitingpositions and through said predetermined angular extent while aclearance surface thereof is in contact with an associated rotatinggrinding surface a predetermined clearance angle and a predeterminedtransversal cutting edge angle are both obtained.

23. Apparatus as set forth in claim 22, wherein a number of cylindricalguiding passages are provided in the guiding element at equal distancesfrom the rotational axis of the wheel and extending parallel theretowhich guiding passages have different diameters for guiding drill bitsof different diameters in relation to the grinding surface.

24. Apparatus as set forth in claim 22, wherein the means of the guidingpassage is a pin in the guiding passage the size of which corresponds tothe intended angle between the main cutting surface and the transversalcutting surface of the drill bit.

25. Apparatus as set forth in claim 22 and further including an abutmentunited with the guiding element for determining the postion of the drillbit in relation to the means in the guiding passage and consequently theposition of the angular area in relation to the grinding surface so thatthe clearance surface of the drill bit will obtain the intendedclearance angle when being pressed against the rotating grinding surfacewhile rotating the drill bit within the angular area corresponding tothe clearance surface.

26. Apparatus for grinding spiral drills having two main cutting edgesand having a clearance surface and a flute for each main cutting edge,comprising a rotatable grinding wheel of which the grinding surfaceconsists of an internal and an external conical part, means for guidingthe clearance surfaces of the main cutting edges relatively to thegrinding surface of the wehel, said means having means for guiding thedrill so that the axis of the drill is parallel to and located at adistance from the axis of the grinding wheel which is equal to theradius of the circular intersection between the internal and theexternal conical part of the grinding surface, at least one first stopmeans for engaging the drill and thereby preventing rotation of thedrill about its axis in one direction beyond a first limiting positionand at least one second stop means for engaging the drill and therebypreventing rotation of the drill about its axis in a direction oppositeto said one direction beyond a second limiting position, said first andsecond stop means being so arranged with respect to one another and to adrill in said guiding means as to be operable to limit rotary movementof the drill about its axis to a predetermined angular extent betweensaid first and second limiting positions such that when said drill isrotated between said limiting positions and through said predeterminedangular extent while a clearance surface thereof is in contact with anassociated rotating grinding surface a predetermined clearance angle anda predetermined transversal cutting edge angle are both obtained.

27. Apparatus as claimed in claim 26, wherein the grinding wheel isaxially movable against a resilient force and wherein the means limitingthe rotary movement of the drill about its axis join the axisl movementof the grinding wheel.

28. Apparatus as claimed in claim 26, wherein the distance in thedirection of the axis of the grinding wheel between the means limitingthe rotary movement of the drill and the grinding wheel is adjustable.

29. Apparatus for grinding drills having at least one main cutting edgeand having a flute and a clearance surface for each main cutting edge,comprising a rotatable grinding wheel having a grinding surface, meansfor guiding the clearance surfaces of the main cutting edges relative tothe grinding surface of the wheel, said means having means for guidingthe drill so that the axis of the grinding wheel and the axis of thedrill are located in two mutually fixed straight lines during thegrinding operation at least one first stop means for engaging the drilland thereby preventing rotation of the drill about its axis in onedirection beyond a first limiting position and at least one second stopmeans for engaging the drill and thereby preventing rotating of thedrill about its axis in a direction opposite to said one directionbeyond a second limiting position, said first and second stop meansbeing so arranged with respect to one another and to a drill in saidguiding means as to be operable to limit rotary movement of the drillabout its axis to a predetermined angular extent between said first andsecond limiting positions such that when said drill is rotated betweensaid limiting positions and through said predetermined angular extentwhile a clearance surface thereof is in contact with an associatedrotating grinding surface a predetermined clearance angle and apredetermined transversal cutting edge angle are both obtained.

30. Apparatus as claimed in claim 29, wherein the grinding wheel ismounted for resilience under the influence of the pressure from a drillpressed against the grinding surface, and wherein the means limiting therotary movement of the drill about its axis join the resilient movementof the wheel.

31. Apparatus as claimed in claim 29, wherein the axial travel of thedrill against the resiliently movable grinding wheel is limited by anabutment engaging the clearance surface of the drill bit not engagingwith the grinding surface of the wheel.

32. Apparatus as claimed in claim 30, wherin the distance between themeans limiting the rotary movement of the drill about its axis and thegrinding surface of the wheel is adjustable.

1. Apparatus for grinding drills having at least two main cutting edgesand having a clearance surface for each main cutting edge, comprising arotatable grinding wheel provided with at most two grinding surfaces andat least one set of guiding means for guiding a drill head in relationto the wheel, the guiding means having means for providing anessentially constant operative angle between the geometricallongitudinal axis of the drill and the rotary plane of the wheel andadmitting a rotation of the drill about said axis, at least one firststop means for engaging the drill and thereby preventing rotation of thedrill about its axis in one direction beyond a first limiting positionand at least one second stop means for engaging the drill and therebypreventing rotation of the drill about its axis in a direction oppositeto said one direction beyond a second limiting position, said first andsecond stop means being so arranged with respect to one another and to adrill in said guiding means as to be operable to limit said rotation ofsaid drill to a predetermined angular extent between said first andsecond limiting positions such that when said drill is rotated betweensaid limiting positions and through said predetermined angular extentwhile a clearance surface thereof is in contact with an associatedrotating grinding surface a predetermined clearance angle and apredetermined transversal cutting edge angle are both obtained. 2.Apparatus according to claim 1, wherein each set of guiding meansconsists of a cylindrical guiding passage provided in a guiding elementand said first and second stop means are provided by at least one guidelug having a pair of oppositely disposed abutment margins and beingassociated with the guiding passage for fitting into a flute of a drill,rotation of the drill about its axis in said one direction beyond saidfirst limiting position being prevented by engagement of said drill withone of said abutment margins and rotation of the drill about its axis insaid opposite direction beyond said second limiting position beingprevented by engagement of said drill with the other abutment margin. 3.Apparatus according to claim 2, wherein there is provided a number ofguiding passages and guide lugs associated therewith, which guidingpassages have different diameters for guiding drills of differentdiameters.
 4. Apparatus according to claim 3, further provided withmeans whereby the wheel, by increasing resistance, resiliently recoilsto the pressure exerted by at least one clearance surface urged againstits corresponding grinding surface, and means for so intercepting theadvance of the drill as to determine a substantially steady operativedistance between the tip of the drill and the guide lugs and a stableresilient counterforce of the wheel.
 5. Apparatus according to claim 4,wherein the wheel is provided with one grinding surface and the meansintercepting the advance of the drill consists of an abutment forreceiving the clearance surface not engaging the grinding surface. 6.Apparatus according to claim 5, wherein the abutments are united in oneabutment element having a stop face advancing helically in the directionof the rotational axis of the wheel at a common distance from said axis,and wherein the guiding passages are so distributed according to theirdiameters over said stop face that a drill, inserted into itsappropriate guiding passage and urged onto the stop face, will cause thewheel to recoil a distance which is so increased by increased drilldiAmeter that the resilient counterforce of the wheel will produceapproximately the same grinding pressure for any drill that isreceivable.
 7. Apparatus according to claim 6, further provided withmeans whereby the distance between the stop face and the guide lugs canbe varied.
 8. Apparatus according to claim 1, wherein the wheel isprovided with two conical grinding surfaces meeting along a circularborder at an angle appropriate to the point angle of the drill. 9.Apparatus according to claim 8, wherein there is a slight clearancebetween the grinding surfaces along the meeting circular border of thesesurfaces.
 10. Apparatus according to claim 8, wherein each set ofguiding means consists of a cylindrical guiding passage provided in aguiding element and said first and second stop means are provided by atleast one guide lug having a pair of oppositely disposed abutmentmargins and being associated with the guiding passage for fitting intothe flute of a drill, rotation of the drill about its axis in said onedirection beyond said first limiting position being prevented byengagement of said drill with one of said abutment margins and rotationof the drill about its axis in said opposite direction beyond saidsecond limiting position being prevented by engagement of said drillwith the other abutment margin.
 11. Apparatus according to claim 10,wherein is provided a number of guiding passages and guide lugsassociated therewith, which guiding passages have different diametersfor guiding drills of different diameters.
 12. Apparatus according toclaim 11, wherein there is a slight clearance between the grindingsurfaces along the meeting circular border of these surfaces. 13.Apparatus according to claim 12, further provided with means whereby thedistance between the grinding surfaces and the guide lugs is adjustable.14. Apparatus for grinding spiral drill bits having at least one maincutting surface and having a clearance surface and a flute for each maincutting surface, comprising a rotatable grinding wheel having a grindingsurface and means for connecting the wheel to a driving device and meansfor guiding a drill bit in relation to the grinding surface, the guidingmeans having means providing a constant angle between the geometricallongitudinal axis of the drill and the grinding surface during thegrinding operation, at least one first stop means for engaging the drilland thereby preventing rotation of the drill about its axis in onedirection beyond a first limiting position and at least one second stopmeans for engaging the drill and thereby preventing rotation of thedrill about its axis in a direction opposite to said one directionbeyond a second limiting position, said first and second stop meansbeing so arranged with respect to one another and to a drill in saidguiding means as to be operable to limit the rotational movement of thedrill bit to a predetermined angular extent between said first andsecond limiting position such that when said drill is rotated betweensaid limiting positions and through said predetermined angular extentwhile a clearance surface thereof is in contact with an associatedrotating grinding surface a predetermined clearance angle and apredetermined transversal cutting edge angle are both obtained. 15.Apparatus for grinding spiral drill bits having at least one maincutting surface, a transversal cutting surface intersecting the maincutting surface and one clearance surface and a flute for each maincutting surface, comprising a rotatable wheel having a bowl-shapedconical grinding surface and having means for connecting the wheel to adriving device, a guiding element fixed in relation to the rotationalaxis of the wheel, a number of cylindrical guiding passages havingdifferent diameters one of which is largest and one of which is smallestprovided in the guiding element at equal distances from the rotationalaxis of the wheel and extending in parallel thereto, for guiding drillbits of different diameters in relation to the grinding surface, guidingpins in the guiding passages adapted to engage each with one of theflutes of the drill bits in order to limit the rotational movement ofthe drill bits between two limiting positions corresponding to thepoints of engagement of said flutes and said pins, said pins being soarranged with respect to one another and to a drill bit in said guidingpassage as to be operable to limit said rotation to a predeterminedangular extent between said limiting positions such that when said drillis rotated between said limiting positions and through saidpredetermined angular extent while a clearance surface thereof is incontact with an associated rotating grinding surface a predeterminedclearance angle and a predetermined transversal cutting edge angle orboth obtained and an abutment united with the guiding element fordetermining the position of the drill bits in relation to the guidingpins.
 16. Apparatus as claimed in claim 15, wherein the wheel is mountedfor resilience in an axial direction under the influence of the pressurefrom a drill bit pressed against the grinding surface, the pressure ofthe drill bit against the grinding surface being limited by the abutmentfor providing a constant grinding pressure.
 17. Apparatus as claimed inclaim 15, wherein the guiding passages are of essentially the samediameter as the drill bit.
 18. Apparatus as claimed in claim 15, whereinthe guiding pins are disposed diametrically opposite each other in theguiding passage and extend inwards approximately one fourth of a guidingpassage diameter towards the center of the guiding passage and beingeach provided with two straight abutments margins extending along twodifferent diameters of the guiding passage forming an angle of 60* witheach other.
 19. Apparatus as claimed in claim 15, wherein the distancebetween the abutment and the guiding pins in the direction of thegeometrical axis of the wheel is adjustable in order to providedifferent clearance angles for the clearance surfaces of the drill bits.20. Apparatus as claimed in claim 15, wherein the abutment is common toall guiding passages and extends along a helical turn, the center axisof which coincides with the rotational axis of the wheel and the radiusof which is slightly shorter than the radius of the circle cutting thecenter axes of all guiding passages.
 21. Apparatus as claimed in claim15, wherein the largest guiding passage is directed towards that pointof the abutment which is nearest to the grinding surface, while thesmallest guiding passage is directed towards the point that is mostremote therefrom, while the other guiding passages are distributedtherebetween according to their diameters.
 22. Apparatus for grindingdrills having at least one main cutting surface and one clearancesurface and a flute for each cutting surface comprising a rotatablewheel having a conical grinding surface, means connected to the wheelfor driving the wheel, a guiding element, at least one cylindricalguiding passage provided in the guiding element for guiding drill bitsin relation to the grinding surface, at least one first stop means inthe guiding passage for engaging a flute of a drill within the guidingpassage and thereby preventing rotation of the drill about its axis inone direction beyond a first limiting position and at least one secondstop means in the guiding passage for engaging a flute of the drill andthereby preventing rotation of the drill about its axis in a directionopposite to said one direction beyond a second limiting position, saidfirst and second stop means being so arranged with respect to oneanother and to a drill within the guiding passage as to be operable tolimit the rotational movement of the drill to a predetermined angularextent between said first and second limiting positions such that whensaid drill is rotated between said limiting positions and through saidpredetermined angular extent while a clearance surface thereof is incontact witH an associated rotating grinding surface a predeterminedclearance angle and a predetermined transversal cutting edge angle areboth obtained.
 23. Apparatus as set forth in claim 22, wherein a numberof cylindrical guiding passages are provided in the guiding element atequal distances from the rotational axis of the wheel and extendingparallel thereto which guiding passages have different diameters forguiding drill bits of different diameters in relation to the grindingsurface.
 24. Apparatus as set forth in claim 22, wherein the means ofthe guiding passage is a pin in the guiding passage the size of whichcorresponds to the intended angle between the main cutting surface andthe transversal cutting surface of the drill bit.
 25. Apparatus as setforth in claim 22 and further including an abutment united with theguiding element for determining the postion of the drill bit in relationto the means in the guiding passage and consequently the position of theangular area in relation to the grinding surface so that the clearancesurface of the drill bit will obtain the intended clearance angle whenbeing pressed against the rotating grinding surface while rotating thedrill bit within the angular area corresponding to the clearancesurface.
 26. Apparatus for grinding spiral drills having two maincutting edges and having a clearance surface and a flute for each maincutting edge, comprising a rotatable grinding wheel of which thegrinding surface consists of an internal and an external conical part,means for guiding the clearance surfaces of the main cutting edgesrelatively to the grinding surface of the wehel, said means having meansfor guiding the drill so that the axis of the drill is parallel to andlocated at a distance from the axis of the grinding wheel which is equalto the radius of the circular intersection between the internal and theexternal conical part of the grinding surface, at least one first stopmeans for engaging the drill and thereby preventing rotation of thedrill about its axis in one direction beyond a first limiting positionand at least one second stop means for engaging the drill and therebypreventing rotation of the drill about its axis in a direction oppositeto said one direction beyond a second limiting position, said first andsecond stop means being so arranged with respect to one another and to adrill in said guiding means as to be operable to limit rotary movementof the drill about its axis to a predetermined angular extent betweensaid first and second limiting positions such that when said drill isrotated between said limiting positions and through said predeterminedangular extent while a clearance surface thereof is in contact with anassociated rotating grinding surface a predetermined clearance angle anda predetermined transversal cutting edge angle are both obtained. 27.Apparatus as claimed in claim 26, wherein the grinding wheel is axiallymovable against a resilient force and wherein the means limiting therotary movement of the drill about its axis join the axisl movement ofthe grinding wheel.
 28. Apparatus as claimed in claim 26, wherein thedistance in the direction of the axis of the grinding wheel between themeans limiting the rotary movement of the drill and the grinding wheelis adjustable.
 29. Apparatus for grinding drills having at least onemain cutting edge and having a flute and a clearance surface for eachmain cutting edge, comprising a rotatable grinding wheel having agrinding surface, means for guiding the clearance surfaces of the maincutting edges relative to the grinding surface of the wheel, said meanshaving means for guiding the drill so that the axis of the grindingwheel and the axis of the drill are located in two mutually fixedstraight lines during the grinding operation at least one first stopmeans for engaging the drill and thereby preventing rotation of thedrill about its axis in one direction beyond a first limiting positionand at least one second stop means for engaging the drill aNd therebypreventing rotating of the drill about its axis in a direction oppositeto said one direction beyond a second limiting position, said first andsecond stop means being so arranged with respect to one another and to adrill in said guiding means as to be operable to limit rotary movementof the drill about its axis to a predetermined angular extent betweensaid first and second limiting positions such that when said drill isrotated between said limiting positions and through said predeterminedangular extent while a clearance surface thereof is in contact with anassociated rotating grinding surface a predetermined clearance angle anda predetermined transversal cutting edge angle are both obtained. 30.Apparatus as claimed in claim 29, wherein the grinding wheel is mountedfor resilience under the influence of the pressure from a drill pressedagainst the grinding surface, and wherein the means limiting the rotarymovement of the drill about its axis join the resilient movement of thewheel.
 31. Apparatus as claimed in claim 29, wherein the axial travel ofthe drill against the resiliently movable grinding wheel is limited byan abutment engaging the clearance surface of the drill bit not engagingwith the grinding surface of the wheel.
 32. Apparatus as claimed inclaim 30, wherin the distance between the means limiting the rotarymovement of the drill about its axis and the grinding surface of thewheel is adjustable.